1. Field of the Invention
The invention disclosed herein relates to measuring force, gravity, pressure and properties of materials in a borehole.
2. Description of the Related Art
In exploration for hydrocarbons, it is important to make accurate measurements of properties of geologic formations. In particular, it is important determine the various properties with a high degree of accuracy so that drilling resources are used efficiently.
Generally, oil and gas are accessed by drilling a borehole into the subsurface of the earth. The borehole also provides access for taking measurements of the geologic formations.
Well logging is a technique used to take measurements of the geologic formations from the borehole. In one embodiment, a logging instrument is lowered on the end of a wireline into the borehole. The logging instrument sends data via the wireline to the surface for recording. Output from the logging instrument comes in various forms and may be referred to as a “log.” Many types of measurements are made to obtain information about the geologic formations. One type of measurement involves determining gravitational force or gravity.
Measurements of gravity can be used to determine information related to the mass of a surrounding formation. For example, measurements of gravity can be used to measure oil depletion in the surrounding formation as water replaces the oil. When water replaces oil in the formation, the mass of the formation and, therefore, a gravitational force exerted by the formation will increase because water is denser than oil.
It is also important to measure parameters in the borehole that may affect drilling operations. One important measurement is pressure within the borehole drilling mud. For safety and environmental concerns, the pressure of drilling mud is maintained at a pressure higher than any pore fluid pressure of any open formation traversed by the borehole. Generally, the density of the drilling mud is important to know in order to maintain the desired pressure of the drilling mud. The density can be determined by measuring the pressure of the borehole fluid at incremental depths to determine the pressure gradient and, therefore, the mud density over each interval.
Accurate measurements of formation characteristics and borehole parameters require accurate measurements of force, gravity and pressure.
Another type of measurement involves performing optical spectroscopy on a material in the borehole such as a formation fluid. Certain types of optical spectroscopy require light of various wavelengths. Due to spatial constraints in the borehole, it is advantageous to have a single light source provide the light.
Therefore, what are needed are techniques for making accurate measurements of force, gravity, pressure and material properties in a borehole.